1. Field of the Invention
The present invention relates to a time correction system in a calculator system and, more specifically, to a time correction system in a cluster system.
2. Description of the Related Art
In a system in which a plurality of calculators are connected via a communication network, time in a clock controlled within each calculator becomes gradually shifted from the standard time (reference time) or it becomes relatively shifted between a plurality of the calculators due to various factors. Thus, it is necessary to perform the time correction processing for correcting the time difference in the clocks of each calculator to meet the standard time.
In a system in which a plurality of calculators is connected via a communication network, NTP (Network Time Protocol) is a widely well-known technique for adjusting the time in the clocks of each calculator.
In the NTP, there is a logical hierarchy, for communication using the NTP, in the relation between a plurality of calculators connected to the communication network. A calculator (NTP client), which requires time correction, makes an access (inquiry about time information for time correction) only to the NTP server within the same hierarchy or the hierarchy of one higher rank.
The NTP client obtains the time information from the NTP server and adjusts the time of the clock in the own device. The NTP server of the higher hierarchy holding the standard time information provides the standard time information to the NTP client of the lower hierarchy in response to the access. Moreover, in the highest hierarchy (primary) NTP server in which the standard time (reference time) can be directly referred and provided, the standard time information is referred and provided by means of cesium atom clock, GPS and the like.
NTP is a technique designed not to concentrate accesses on one server for correcting time between a plurality of calculators connected via a communication network. Also, it is designed to improve the accuracy of time synchronization by canceling communication delay time due to circuits.
As the related art, Japanese Patent Application Laid-open No. 2000-349791 discloses a technique for achieving the overall time correction processing in which, in LAN, an NTP client (representative NTP client) among a plurality of calculators makes an access (time inquiry) to the NTP server representatively and the representative NTP client and a group of other NTP clients perform time correction processing (as the second step of the overall processing) separately from the above-described access, so that the NTP server does not receive accesses from a plurality of NTP servers.
Recently, there is an increasing demand for a cluster system (clustering system). The cluster system is a system for executing services and work by building a system by clusters of a plurality of calculators.
In the above-described cluster system, it is also necessary to perform a prescribed time correction processing in regards to time (clock) held by each device constituting the cluster. Generally, in the cluster system, performance and fault resistance are improved by allotting logical operating state (operation mode) to each device according to a prescribed system operation policy corresponding to use of processing so as to operate the devices in cooperation.
A problem will be generated when the above-described related art regarding time correction is applied to the cluster system. The problem will be described below. An access (inquiry about standard time information) is made to a device or means which provides the standard time information placed outside the cluster system having any one of the devices in the cluster system as a representative device. The device, which obtains the standard time information through communication with outside as the representative within the cluster system, is referred to as the representative device in the followings.
First, the representative device obtains the standard time information from an outside device and performs time correction of the inside clock (=a first time correction processing). Further, devices other than the above-described representative device in the cluster performs time correction (=a second time correction processing) by referring to the time of the representative device (the time which has been corrected to the standard time in the above-described first time correction processing). Through those two of time correction processing, the time of each device in the cluster is synchronized. This processing is repeated in the cluster system at a prescribed timing.
Incidentally, the cluster system is a system with a characteristic in which logical operating state (operation mode) such as operational system (act) and standby system (standby) are allotted to each device according to a prescribed policy so as to change (switch the system) the operational system and standby system according to the condition for executing the overall services and work. Thus, there is a problem regarding how to adapt the factors including the operating state of the devices and the irregular change/switching to the time correction processing.
Especially, it is a problem regarding how to adapt the factors including the operating state of the devices and the irregular change/switching to the execution of time correction processing in the cluster system through providing the above-described representative device.
In the basic operation policy of the cluster system, the operational system is a system which directly executes services and work of the system while the standby system stands by in case when the operational system is down (function stopped) and the like without directly executing services and work of the system to be operated and switched to be a new operational system when necessary. There may be a case where a function of taking over the former operational system is added if high availability is desired.
There are devices of operational system and standby system within the cluster system. Provided the device of either system (operating state) is set to be the representative device and performs the time correction processing, there generates irregular switching of systems (change of the operating state) in the cluster system. Thus, there is a problem regarding how to deal with the representative device according to the switching and changing of the system.
As described, when the representative device is set in the cluster system for performing the time correction processing as the cluster system, there is a problem regarding how to perform appropriate time correction processing through adapting the operating state of each device in the cluster and the irregular change/switching.
For example, Japanese Patent Application Laid-open No. 2001-305256 discloses a time synchronizing system in a plurality of calculators. Specifically, it discloses processing capable of switching a master (hot) and a slave (standby) by duplicating the processing unit in order to increase the reliability of the time synchronization program.
However, the duplicated processing and hot/standby structure is only for the processing unit (time synchronization program) for performing time synchronizing processing and not specifically directed to the processing as the cluster system. Thus, it differs from the object of the system of the present invention, which is to provide the time correction processing as the cluster system comprising the operating state of the devices such as operational system and standby system.